1. Field of the Invention
The invention relates to a method of determining new luminance value data based on original luminance value data to be displayed on a matrix display device, where the luminance value data are coded in sub-fields, the sub-fields comprising a group of most significant sub-fields, and a group of least significant sub-fields, wherein a common value for the least significant sub-fields is determined for a set of lines.
The invention also relates to a matrix display device comprising means for determining new luminance value data based on original luminance value data to be displayed on a matrix display device in accordance with said method.
The invention may be used, e.g., in plasma display panels (PDPs), plasma-addressed liquid crystal panels (PALCs), liquid crystal displays (LCDs), Polymer LED (PLEDs), Electroluminescent (EL), television sets used for personal computers, and so forth.
2. Description of the Related Art
A matrix display device comprises a first set of data lines (rows) rl . . . rN extending in a first direction, usually called the row direction, and a second set of data lines (columns) cl . . . cM extending in a second direction, usually called the column direction, intersecting the first set of data lines, each intersection defining a pixel (dot).
A matrix display further comprises means for receiving an information signal comprising information on the luminance value data of lines to be displayed and means for addressing the first set of data lines (rows rl, . . . rN) depending on the information signal. Luminance value data are hereinafter understood to be the gray level in the case of monochrome displays, and each of the individual levels in color (e.g., RGB) displays.
Such a display device may display a frame by addressing the first set of data lines (rows) line by line, each line (row) successively receiving the appropriate data to be displayed.
In order to reduce the time necessary for displaying a frame, a multiple line addressing method may be applied. In this method, more than one, usually two, neighboring, and preferably adjacent, lines of the first set of data lines (rows) are simultaneously addressed, receiving the same data. This so-called double-line addressing method (when two lines are simultaneously addressed) effectively allows speed-up of the display of a frame, because each frame requires less data, but mostly at the expense of a loss of the quality with respect to the original signal, because each pair of lines receives the same data, which can induce a loss of resolution and/or sharpness due to the duplication of the lines.
For the above-mentioned matrix display panel types, the generation of light cannot be modulated in intensity to create different levels of gray scale, as is the case for CRT displays. On these matrix display panel types, gray levels are created by modulating in time: for higher intensities, the duration of the light emission period is increased. The luminance data are coded in a set of sub-fields, each having an appropriate duration or weight for displaying a range of light intensities between a zero and a maximum level. The relative weight of the sub-fields may be binary (i.e., 1, 2, 4, 8, . . . ) or not. This sub-field decomposition, described here for gray scales, will also apply hereinafter to the individual colors of a color display.
In order to reduce loss of resolution, line doubling can be done for, e.g., some less significant sub-fields (LSB sub-fields). Some LSB sub-fields correspond to a less important amount of light, and partial line doubling will give less or no loss in resolution.
The use of partial line doubling should be effective. Only a few LSB sub-fields doubled would yield a little gain of time. Too many sub-fields doubled would yield an unacceptable loss of picture quality.
Another aspect that influences the quality is the calculation method of the new data of doubled sub-fields. Different calculation methods giving different results can be used. The method used should give the best picture quality, as seen by the observer""s eyes.
As the LSBs are doubled in partial line doubling, the value of the LSB data for two neighboring or adjacent lines must be the same. Several methods can be used for the calculation of these data, such as:
The LSB data of odd lines is used on the adjacent even lines (simple copy of bits);
The LSB data of even lines is used on the neighboring or adjacent odd lines (simple copy of bits);
The average LSB data of each pair of pixels is used for both new LSB values;
The sub-fields data of the line with the lowest luminance is copied to the other line;
The doubled sub-fields are determined as to minimize the total error.
These methods allow a reduction of the addressing time, at the expense of a loss of resolution. However, a difference, and in some instances a large difference, may exist between the original luminance values to be displayed and the new luminance values actually displayed.
In International Patent Application No. WO 99/49448, corresponding to U.S. Pat. No. 6,373,477, a method is disclosed wherein so-called motion compensation is performed for sub-fields in a plasma display panel.
It is an object of the present invention to improve upon the above prior art method, especially with respect to reducing the addressing time in such a panel.
The present invention provides a method of driving a display wherein a field period for the display is divided into several sub-fields, and wherein:
a number of sub-fields values are compensated for motion artefacts; and
at least one of the sub-fields in subsequent lines is addressed simultaneously.
An advantage of this invention is that by combining steps for compensating sub-field values for motion artefacts with steps for addressing sub-fields in subsequent lines simultaneously, it is possible to achieve both a richer image with more contrast and a preferable image with less visible artefacts. By applying steps for addressing the sub-fields in subsequent (partial line doubling, PLD), it is achieved that addressing the sub-fields is done in less time thereby enabling, e.g., longer sustain periods per sub-field, which improves the amount of emitted light and thereby the brightness of the image. By applying steps for compensating sub-field values for motion artefacts, the occurrence of motion artefacts, which are visible in the image when objects move, are minimized. In a preferred embodiment of the invention, the PLD data calculation is performed first, whereafter only the non-doubled sub-fields are motion compensated while the line doubled sub-fields are not compensated. In a further preferred embodiment, motion compensation is applied first, whereafter the partial line doubling data calculation is executed.
In a further preferred embodiment, the partial line doubling is performed first for all sets of lines 2N+1 and 2N+2 (the xe2x80x9coddxe2x80x9d set) and for all sets of lines 2N and 2N+1 (the xe2x80x9cevenxe2x80x9d set), where N is an integer number. Herewith, it is preferred that the size of a vertical blocking of a motion vector is a multiple of a number of partial line doubling, as is further explained in connection with FIGS. 9, 10 and 11. In this embodiment, the multiple is preferably a multiple of the number of lines in which the same sub-field data is copied to and that is addressed simultaneously. In specific embodiments, copying is performed over a larger number of lines, e.g., when sub-fields of four lines are copied, there are four sets starting at a 1st, 2nd, 3rd and 4th line.
In further embodiments, the partial line doubling comprises steps for minimizing the error, averaging the data or copying the data during the data calculation. Especially steps for minimizing the error result in a better picture. Advantages of the copying of the date are that less calculation time is needed. An advantage of the averaging method is that a better picture is achieved than using the copying method.
In further embodiments, values of the sub-fields depend on a shift of the highest doubled sub-field. Furthermore, an embodiment is provided in which values of the sub-fields depend on a shift of the lowest non-doubled sub-field.